Transportation modes of pollen in surface waters in the South China Sea and their environmental significance

• The distribution of surface water pollen is influenced by sea currents and rivers.
• The number of surface water pollen has little relationship with sampling seasons.
• The number of surface water pollen is directly proportional to deposition rate.
• The main surface sediment pollen transmission factor in autumn is wind.
• The surface sediment pollen transmission factors are wind and currents in winter.

This is the first study to determine the main source of pollen in surface-water samples from the South China Sea. Forty-four surface-water samples were taken at a water depth of 5 m in the South China Sea 2010 and 2011. Palynological analyses show that the distribution of pollen in surface water is strongly influenced by ocean currents and rivers, particularly in the northern South China Sea. The Pearl River, the surface boundary current, and the Kuroshio Current are the main suppliers of pollen. The number of pollen and spores in the surface-water samples from the South China Sea shows little relationship with sampling seasons but is proportional to the sediment deposition rate. The number of airborne pollen and total concentrations of airborne pollen reveal a close relationship with the sampling season, wind direction, and sampling locations. There is no close relationship between the total pollen concentration of surface sediment and the sediment deposition rate. Therefore, we conclude that the main pollen transport factor of seabed-surface sediment samples in the South China Sea during autumn is wind, whereas both wind and currents are the main transport factors in winter because the pollen number of airborne pollen samples is significantly higher than that of sea surface-water samples in autumn. In addition, the number of pollen in airborne samples is as small as that in sea surface-water samples in winter.